Recently, the use of flat display panels has increased, a liquid crystal display (LCD) being a representative flat display panel.
Generally, unlike existing cathode ray tube (CRT) displays, such an LCD requires a backlight module for providing light uniformly to an entire screen.
In an existing backlight unit, a lamp (i.e. a linear light source) and a lamp reflection plate for reflecting light generated by the lamp are disposed on one side of a light guide plate for converting the light generated by the lamp into planar light, and a reflection sheet for preventing a leakage of light is disposed on a lower portion of the light guide plate.
A prism sheet having a plurality of linear prisms having a triangular shape protruding upward is disposed on the light guide plate to collect scattered light. Since linear prisms are disposed perpendicularly to each other, two prism sheets may collect light beams reflected in different directions.
However, since such an existing backlight requires two prism sheets, production costs may be increased, a number of processes may be increased, and there may be a limit in reducing the thickness of a backlight unit.
In order to overcome the limitations, recently, a prism sheet having a reverse prism shape, in which a prism peak 12 protrudes toward a light guide plate 3, i.e. in a downward direction, opposite to a direction disclosed in the related art, has been developed. Here, the prism peak 12 formed on the prism sheet 10 has a triangular shape, is repeated along the lower surface of the prism 10, and protrudes downwardly.
Since light incident from the light guide plate 3 is totally reflected and transferred upwardly by an inner side surface of the prism peak 12, the prism sheet 10 having a reverse prism shape has advantages in terms of thickness and manufacturing costs, as compared to a case in which two prism sheets are used.
However, since incident light is collected in one direction when reflected by the prism peak 12, brightness is improved, but a viewing angle is narrowed when the prism sheet 10 having the reverse prism shape is used in a backlight unit of an LCD.